yubikey-agent: fix systemd unit

I was getting problems with the unit failing to start due to NAMESPACE
or CAPABILITIES permissions.

Upstream now provides a systemd unit file in the repo, we should use that
one, and that one works for me.

pkgs/tools/security/yubikey-agent/default.nix

@@ -2,13 +2,13 @@
 
 buildGoModule rec {
   pname = "yubikey-agent";
-  version = "0.1.3";
+  version = "unstable-2021-02-18";
 
   src = fetchFromGitHub {
     owner = "FiloSottile";
     repo = pname;
-    rev = "v${version}";
-    sha256 = "07gix5wrakn4z846zhvl66lzwx58djrfnn6m8v7vc69l9jr3kihr";
+    rev = "8cadc13d107757f8084d9d2b93ea64ff0c1748e8";
+    sha256 = "1lklgq9qkqil5s0g56wbhs0vpr9c1bd4ir7bkrjwqj75ygxim8ml";
   };
 
   buildInputs =
@@ -25,7 +25,7 @@ buildGoModule rec {
     substituteInPlace main.go --replace 'notify-send' ${libnotify}/bin/notify-send
   '';
 
-  vendorSha256 = "128mlsagj3im6h0p0ndhzk29ya47g19im9dldx3nmddf2jlccj2h";
+  vendorSha256 = "1zx1w2is61471v4dlmr4wf714zqsc8sppik671p7s4fis5vccsca";
 
   doCheck = false;
 
@@ -42,7 +42,7 @@ buildGoModule rec {
   # See https://github.com/FiloSottile/yubikey-agent/pull/43
   + lib.optionalString stdenv.isLinux ''
     mkdir -p $out/lib/systemd/user
-    substitute ${./yubikey-agent.service} $out/lib/systemd/user/yubikey-agent.service \
+    substitute contrib/systemd/user/yubikey-agent.service $out/lib/systemd/user/yubikey-agent.service \
       --replace 'ExecStart=yubikey-agent' "ExecStart=$out/bin/yubikey-agent"
   '';